1. Field of the Invention
The present invention relates to a secondary battery, and more particularly, to enhanced collector and electrode structures and a secondary battery adopting the same.
2. Description of the Related Art
There are various types of rechargeable secondary batteries including a nickel-cadmium (Nixe2x80x94Cd) battery, a lead acid battery, a nickel metal hydride (Ni-MH) battery, a lithium (Li) ion battery, a Li polymer batter, a metal Li secondary battery and the like.
In particular, rechargeable secondary batteries including Li have high energy density to weight ratio compared to the Nixe2x80x94Cd battery or the Ni-MH battery, so their use is gradually expanding. The Li secondary battery is classified into a Li ion battery using a liquid electrolyte and a Li polymer battery using a polymer solid electrolyte, according to the type of electrolyte.
FIG. 1 shows an example of the Li polymer battery. Referring to FIG. 1, the Li polymer battery comprises an electrode assembly 11 in which a positive plate and a negative plate are stacked with a separator interposed therebetween, and a case 12 sealing the electrode assembly 11. Also, electrode tabs 13 are connected to connection tabs 13a of the positive and negative plates, the electrode tabs 13 protruding outside the case 12.
The positive and negative plates are manufactured by laminating a collector formed of copper (Cu) or aluminum (Al) with sheets respectively made of negative and positive active materials. The separator is interposed between the positive and negative plates, a plasticizer is extracted from the electrode assembly including the positive and negative plates and the separator, and then an electrolyte is injected into the empty space from which the plasticizer has been extracted.
The collector is formed of expanded metal in order to increase the adhesion with the active material sheets and to increase conductivity by increasing the contact area.
However, in manufacturing the electrode through a continuous process, the tensile force to the expanded metal acts in the same direction as that of elongation for manufacturing the expanded metal, so the collector deforms by such elongation. Thus, the expanded metal is not suitable for electrodes produced through continuous mass production systems. Also, the expanded metal is as thick as about 30 xcexcm and the deviation in thickness thereof reaches 10 xcexcm, so it is difficult to control the thickness when attaching the active material sheet. Also, when an electrode plate manufactured by attaching the active material sheet to a collector is cut to a predetermined size, there is burring at the cut part, thereby electrical shorting the positive and negative plates.
In order to solve these problems, a punched metal has been used for collectors. However, openings formed in the punched metal are very critical to the properties of the electrode assembly. That is, if the openings of the punched metal are too small, electrical conductivity is improved while smooth extraction of a plasticizer is not guaranteed. Otherwise, the electrical conductivity is reduced even though the plasticizer can be easily extracted.
To solve the above problems, it is an object of the present invention to provide a collector, an electrode and a secondary battery adopting the same, in which deformation of the collector, caused by a tensile force during a continuous manufacturing process, can be minimized, electrical conductivity of the collector is good and a plasticizer can be smoothly extracted from the collector.
According to an aspect of the object, the present invention provides a collector of a battery, comprising a thin plate member in which a plurality of through holes are formed in a predetermined pattern with a uniform rib width.
Preferably, the through holes have a circular or regular polygonal shape.
According to another aspect of the object, the present invention provides an electrode of a battery, comprising: a collector formed as a flat member in which a plurality of through holes are formed in a predetermined pattern; and an active sheet attached to at least one side of the collector, wherein assuming that the thickness of the collector is T1 and the sum of the thicknesses of the collector and the active material sheet is T2, T2xe2x89xa66.32xc3x97T1.
Assuming that the size of the through holes is M and the sum of the thicknesses of the collector and the active material sheet is T2, preferably, 3.75T2xe2x89xa6Mxe2x89xa618.75T2.
Assuming that the pitch between the through holes is P and the sum of the thicknesses of the collector and the active material sheet is T2, preferably, 1.2Mxe2x89xa6Pxe2x89xa61.6M.
According to still another aspect of the object, the present invention provides a secondary battery comprising: an electrode assembly having electrodes obtained by attaching an active material sheet to at least one side of a flat collector with a plurality of through holes formed in a predetermined pattern, and a separator interposed between the electrodes; a case for sealing the electrode assembly; and tabs connected to terminals of the electrode assembly and extended outwards the case, wherein the through holes have a regular polygonal shape and the rib widths among the through holes are equal.